This invention concerns a chamber for the treatment of cells in an electrical field, in which a space formed from electrically nonconducting walls is provided to hold the suspension containing the cells, into which extend at least two electrodes in such a way that a region bounded by them is formed between the electrodes, the cells being exposed to an electrical field developed between the electrodes.
A process is known from German Pat. No. 24 05 119 for the treatment of cells in an electrical field, in which the membrane of cells is pierced by applying an electrical field whose strength is 10.sup.3 to 10.sup.5 V/cm. The increase of permeability of the cell membrane thus produced makes it possible to interchange substances through the membrane without impairing the viability of the cells, since the increase of the permeability is reversible in a simple procedural step after the interchange of the substances. It is also possible in this way, for example, to incorporate genes or enzymes into the cells.
The process for increasing the permeability of the cell membrane disclosed by the aforementioned Patent can also be used for the fusion of cells.
Two cells in a suspension, if they touch one another and if there is a close contact between the membranes of the two cells, should fuse with one another, since the fundamental units in the membrane are mobile. However, such a spontaneous fusion of cells is extremely seldom, or never, observed under natural conditions. The fertilization of an egg cell by a sperm cell in sexual propagation represents a known exception. The spontaneous fusion is prevented by the negative charge of the phospholipids and other membrane components. It leads to the repulsion of the cells when they have approached to within a small distance of one another. However, cell fusion requires the two membranes to be able to approach one another to a distance of less than 10.sup.-7 cm.
The fusion of cells carried out by technical means, or synthetically, can be used for a broad range of applications. Thus, it is of great interest for biological-medical research to fuse a large number of cells with one another. With a suitable size of the large cells formed by the fusion of several or optionally many cells--for example, 1,000 to 10,000 blood corpuscles--microelectrodes, micro pressure-measurement probes, and other sensors can then be introduced into the large cell without irreversible destruction of the membrane. The technique of measuring directly a number of cell and membrane functions through the sensors is important for clinical diagnoses, for example in the early recognition of illnesses and generally for basic research.
The technique of fusion of cells can also be used for the formation of hybrid cells by the fusion of two cells of different origin, which should not be too far removed from one another in evolution. Cell hybrids can thus be formed from plant cells, from which whole plants can again be grown, or cell hybrids from animal cells through which the monoclonal antibodies can be obtained, such as those against tumors and leukemia. An example which can be mentioned is the fusion of a lymphocyte cell with a myeloma cell, which is of great interest in particular from the medical and pharmaceutical viewpoints. Certain lymphocytes form antibodies against foreign substances in the organism, for example against a foreign protein which has been injected into the bloodstream. If the lymphocytes are isolated and fused with a tumor cell such as a myeloma cell, there is a chance that a so-called hybridoma cell will be formed, which has the nature of both parent cells. This cell produces antibodies, specifically only against the foreign substance involved (so-called monoclonal antibodies). It is immortal, and in contrast to a normal differentiated cell such as a lymphocyte, can be propagated permanently in nutrient media.
A process for the fusion of cells of the type mentioned initially is known from Biochimica et Biophysica Acta, 694 (1982), 227-277 (Electric Field-Mediated Fusion and Related Electrical Phenomena, U. Zimmermann). In this known procedure, the progress of which can be observed under the microscope, the membrane contact is produced between at least two cells by the application of an alternating, poorly homogeneous field. Because of polarization processes in the cell, dipoles are produced by the electrical field which mutually attract one another when the cells approach one another during their migration in the electrical field (so-called dielectrophoresis). After the formation of the sets of cells, the disturbances in the membrane structure between neighboring cells are triggered by an electrical breakdown pulse (J. Membrane Biol. 67, 165-182 (1982), Electric Field-Induced Cell-to-Cell Fusion, U. Zimmermann and J. Vienken). According to the models proposed up to now, holes are thus produced in the membrane contact zones of adjacent cells which lead to a cytoplasmic continuum between the two cells and to bridge formation by lipids between the membranes of adjacent cells. The lipid molecules are no longer lined up in their original membrane. As soon as such a bridge has formed, the structure formed, which consists of the cells joined together through the lipid bridges, becomes rounded off for energy reasons.
To carry out this known process, a chamber of the type described initially is used. To form the sets of cells, the electrodes of the chamber are connected to a device for producing an alternating electric field and to a device for producing electrical voltage pulses to produce the electrical breakdown.
In implementing the known process, it is endeavored, if possible, to subject all of the cells present in a suspension to the electrical treatment to increase the effectiveness of the process. This assumes that as many of the cells introduced into the chamber as possible are exposed to the electrical field. The dead zones in the chamber should therefore be as small as possible.
It is the purpose of this invention to describe a chamber of the type mentioned initially, in which a large fraction of the cells introduced into the chamber are exposed to the electrical field. The chamber is also intended to make possible the simultaneous and uniform treatment of a large number of cells.